Refining titanium alloys



July 26, 1960 R. s. DEAN ETAL 2,946,730

REFINING TITANIUM ALLOYS Filed Feb. 9, 1959 M A Um/ 7%. MZ INVENTOILS.

United States atent fiice REFINING TITANIUM ALLOYS ware Filed Feb. 9, 1959, Ser. No. 792,230,

3 Claims. (Cl. 204-64) This invention relates to the electrorefining of titanium in fused baths containing alkalinous metal chlorides, titanium chlorides and dissolved alkalinous metals. This application is a continuation-in-part of our copending application, Serial No. 629,947, filed December 21,1956, and now abandoned. It relates especially to the provision of such baths which can be used at relatively low temperatures for refining titanium alloys, for example, those of manganese, iron and chromium, below their eutectoid temperatures. That is the temperature below which there is no solid solubility of the metals. It relates more especially to baths and refining conditions which produce titanium adherent the cathode substantially entirely in large crystals which drain nearly free of molten salt as described in the copending application of Gullett, Serial No. 592,543, filed June 20, 1956, now Patent No. 2,874,- 454, which latter describes a new structure of titanium deposits, the production of which is one of the objects of this invention. Other objects include the refining of titanium alloys. I

In copending application of Gullett, Serial No. 577,227, filed April 10, 1956, and Dean and Gullett, Serial No. 601,705, filed August 2, 1956, now Patent No. 2,901,410, there are described the refining of titanium alloys in baths containing alkalinous metal chlorides, titanium chlorides and free alkalinous metals. Dean and Resnick, Serial No. 605,231, filed August 20,

' 1956, there are disclosed control procedures for such bath,

and in copending application of Dean, Serial No. 600,039, filed July 25, 1956, now Patent No. 2,909,472, there is disclosed the formation of large crystalsfrom these baths by formation and crystallization of baths supersaturated with respect to titanium and alkalinous metal.

In these applications, there are disclosed the formation of such supersaturated solutions by the provision of the material to be refined in comminutedform, hence very large surface and relatively small cathode surface. We have also disclosed the preferred disposition of anode material and cathode as that of an annular anode surrounding a cylindrical cathode. I

The present invention relates specifically to electrolytes containing strontium chloride, sodium chloride, titanium chlorides and free alkalinous metal. Such electrolytes are within the disclosure of such compositions in copending application, Dean, Serial No. 592,089, filed June 18, 19.56. The present invention relates to specific compositions and co-related operating conditions to refine alloys and to produce the large crystals of the invention.

We are aware that .electrolytescontaining SrCl NaCl and mixtures of TiCl and TiCl having at least 40% TiCl have been disclosed for refining crude titanium. Unless such baths are to be regarded as indefinite in composition, we must assume that the ratio of TiCl to TiCl is determined by the accepted method, total soluble titanium and TiCl determined by hydrogen evolved on acidification as described in Final Report ONR contract NONR 266( 24) Physical Chemistry of NaCl-KCI Melts In copendingapplication of i Containing Dissolved Titanium chlorides, lune 51956,

H. H. Kellog, Project Director.

We have made electrolytes having from 40-100% of the soluble titanium as TiCl as so determined and with 1.5 molar total soluble titanium chlorides and have used same at temperatures from 1000 F.-1800 F. and with anode current densities from .01-.25 amp/sq. cm. and cathode current densities of 1.0-10 amperes/sq. cm. and have not obtained the product of our invention having at least 90% very coarse crystals and less than '1 0% included salt as fully described in the copending application of Gullett, Serial No. 577,227, filed April 10, 1956.

We have now used an electrolyte of preferred composition defined as follows: Base electrolyte 65% SrCl 35% NaCl to which is added titanium chlorides and sodium to produce total soluble titanium 9%. Ti as TiCl by meth- 0d of Final Report ONR Contract 'NoNR 266 (24) 14.9%. Ave. valence, by method of that report, 1.34. Corrected for free alkalinous metal, 2.2. H evol'ved per gram due to free alkalinous metal, 16.2 ml.

The electrolyte composition may vary somewhat from the preferred composition, however, good results require that the variation from the preferred titanium content of 9% should not be more than 12% and the average valence should not vary from the preferred 2.2 by more than 2.15% while the free alkalinous metal which in the preferred condition corresponds to 16.2 ml. hydrogen evolved per gram should not vary more than :7 ml.

Free alkalinous metal is determined by hydrogen evolution in acidified ferric chloride, as described in copending application, Dean and Resnick, previously referred to.

It will be noted that when TlCi2 is determined by the method of Final Report ONR Contract 266(24), the bath contains an amount of titanium as TiCl substantially in excess of total soluble titanium and is obviously not Within the composition range contemplated by the prior art. With this electrolyte, we have found that the large crystals of our invention are obtained only with certain combinations of temperature and anode current density. The following table shows this relationship:

Anode current density Temp. P. less than amps. /sq. cm. 1000 .0001

The cathode current density was 1000-15000 amps/sq. meter. We have found that certain variations are permissible from the preferred electrolyte described. The base electrolyte may vary from:

, Percent SrCl 50-75 NaCl 50-25 T Percent Mn in cathode product 1000" F. 0 1200 F 4.5 1400 F. 6.5 1600 F. 6.0

The maximum figures given here are electrolytes containing 9.0% total soluble titanium.

The analysis of the cathode product other than the Mn content shown inthetable was .01%, N 003%, Fe 002%, C .001%. J -Example I i For the purpose of this example, we use the apparatus in Figure 1. This apparatus consists of a steel pot C, provided with a tight cover E having inlet and outlet for argon F and F1. A packing gland G, for the immersion at the start and elevation after electrolysis of the steel cathode B; A forarninous steel basket D, annularly disposed around the cathode B and connected as anode through an insulator in the lid G by a steel rod A. In this example, we place comminuted crude titanium having the following analysis in the foraminous steel basket:

Percent 0 0.2 Fe 0.5 Mn 8.0

Balance substantially titanium.

The basket contains 2 pounds of the crude titanium having a surface area of 1000 sq. ft. per pound.

We place an electrolyte in the pot consisting of 65% srCl 35% NaCl to which has been added titanium chlorides, and sodium to produce 9% total soluble titanium Percent 0 0.02 Fe 0.001 Mn 5.2

Balance titanium.

Example II "In this example, we proceed as in Example I, except that we comminute the crude titanium to provide 10,000 sq. ft. of total anode surface.

In this example, 95% of thetitanium crystalaggregates on the cathode are coarser than /1 inch average diameter and. only 3% salt isretained with them. Analysis of these coarse crystals after washing on acid and melting in argon shows:

Percent 0 0.02 Fe 0.001 Mn 5.4

Balance titanium.

' Example III Inthis example, we proceed as in Example I, except that we use a temperature of 1000 C. and as anode material, we use a comminuted alloy of crude titanium and manganese with the same analysis as in Example I. Using the procedure of Example I, including the anode surface, we obtain a product on the cathode as described in Example I. This product after washing and melting in argon analyzes: a

We proceed as in Example III except that the anode surface is 100,000 sq. ft. The product in this instance is like that-of Example 11 and has the following analysis when washed and melted in argon:

Percent O -03 Fe QJ 0.001 Mn .01

Balance titanium.

Example V We proceed as in Example II except that a base electrolyte consisting of 65% SrCl NaCl containing 7% total soluble titanium, average valence 2.05 and alkalinous metal equivalent to 9.5 mL/gram is used. The product is the same as that of Example 11 except that it contains 0.1% manganese.

What is claimed is:

1. In a process for electrorefining titanium containing oxygen and at least one element selected from the group consisting of Fe, Cr and Mn in solid solution, in a single phase electrolyte consisting of at least one fused alkalinous chloride and, dissolved therein, lower chlorides of titanium and at least one alkalinous metal, the improvement which consists in maintaining an electrolyte composition of SrCl -75%, balance NaCl, and dissolved'therein 1 about 9% soluble titanium as chloride, average valence about 2.2, and alkalinous metal corresponding to 10-20 ml. of hydrogen per gram of electrolyte evolved in acidificd ferric chloride, at a temperature of 1000 F.-1600 F. and passing direct current through the electrolyte from a comminuted anode of the alloy to be refined at an anode current density dependent on temperature from below .005 amp./sq. cm. at 1600 F. to below .0001 amp/sq.

cm. at 1000 F. to an inert cathode at a cathode current density of from 0.05 to 2.0 amps/sq. cm. whereby to form large crystals of pure titanium, adherent to the cathode.

Temperature, F.:

2. The improved process defined in claim 1, wherein the maximum anode current density employed and the temperature at which the electrolyte is maintained have the relationship.

Anode 0.1)., less than ampJsq. cm.

3. The improved process defined in claim 1, wherein the alkalinous chloride content of the electrolyte consists essentially of SrCl and NaCl' in the approximate weight proportion of 65:35, the electrolyte is maintained at a temperature of about 1400 F., the anode current density is maintained at not to exceed .001 ampere per sq. cm., whereby to produce a crystalline titanium cathode product .of the titanium crystal aggregates of which are coarser than one-fourth inch average diameter.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR ELECTROREFINING TITANIUM CONTAINING OXYGEN AND AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF FE, CR AND MN IN SOLID SOLUTION, IN A SINGLE PHASE ELECTROLYTE CONSISTING OF AT LEAST ONE FUSED ALKALINOUS CHLORIDE AND, DISSOLVED THEREIN, LOWER CHLORIDES OF TITANIUM AND AT LEAST ONE ALKALINOUS METAL, THE IMPROVEMENT WHICH CONSISTS IN MAINTAINING AN ELECTROLYTE COMPOSITION OF SRCL2 50-75%, BALANCE NACL, AND DISSOLVED THEREIN ABOUT 9% SOLUBLE TITANIUM AS CHLORIDE, AVERAGE VALENCE ABOUT 2.2, AND ALKALINOUS METAL CORRESPONDING TO 10-20 ML. OF HYDROGEN PER GRAM OF ELECTROLYTE EVOLVED IN ACIDIFIED FERRIC CHLORIDE, AT A TEMPERATURE OF 1000*F.-1600*F. AND PASSING DIRECT CURRENT/THROUGH THE ELECTROLYTE FROM A COMMINUTED ANODE OF THE ALLOY TO BE REFINED AT AN ANODE CURRENT DENSITY DEPENDENT ON TEMPERATURE FROM BELOW .005AMP/SQ. CM. AT 1600*F. TO BELOW .0001 AMP./SQ. CM. AT 1000*F. TO AN INERT CATHODE AT A CATHODE CURRENT DENSITY OF FROM 0.05 TO 2.0AMPS/SQ. CM. WHEREBY TO FORM LARGE CRYSTALS OF PURE TITANIUM, ADHERENT TO THE CATHODE. 